chore(html-reporter): use button elements for tabs

[triemerge]

Rationale

The html-reporter has its own TabbedPane that was still using <div role="tab"> for tab elements. Since those aren't natively focusable, keyboard users couldn't really reach the retry tabs (Run, Retry #1, etc.) when viewing test results. This converts them to <button> and adds :focus-visible styling, following the same approach from #41434.

[github-actions]

Test results for "MCP"

4 failed
❌ [chromium] › mcp/http.spec.ts:349 › client should receive list roots request @mcp-ubuntu-latest-chromium
❌ [firefox] › mcp/http.spec.ts:349 › client should receive list roots request @mcp-ubuntu-latest-firefox
❌ [webkit] › mcp/http.spec.ts:104 › http transport browser lifecycle (isolated) @mcp-ubuntu-latest-webkit
❌ [webkit] › mcp/http.spec.ts:349 › client should receive list roots request @mcp-ubuntu-latest-webkit

7376 passed, 1122 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

2 failed
❌ [chromium-library] › library/browsercontext-add-init-script.spec.ts:28 › should work without navigation, after all bindings @chromium-ubuntu-22.04-arm-node20
❌ [chromium-library] › library/browsercontext-expose-function.spec.ts:77 › should be callable from-inside addInitScript @chromium-ubuntu-22.04-arm-node20

2 flaky

⚠️ [chromium-library] › library/chromium/chromium.spec.ts:211 › should intercept service worker requests (main and within) `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/chromium/chromium.spec.ts:434 › should produce network events, routing, and annotations for Service Worker (advanced) `@realtime-time-library-chromium-linux`

49056 passed, 1142 skipped

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Merge workflow run.